The Mobility of Actinium Active Deposit Ions

The mobility of the ions in actinium active deposit is determined by drawing them across an air stream having a speed of 20 m/sec., by means of an electric field of over 100 v/cm, and allowing them to deposit on a metal plate. The amount of deposit at various distances along the plate is determined by the ionization it produces through a slit in the wall of an ionization chamber. It is found that two positive ions are present, one of which has a mobility of about 4.35 cm/sec/volt/cm and the other 1.55. The first is greater than that of monomolecular ions of air and the second greater than that of bi-molecular ions of air (Phys. Rev. 24, 1924). The interpretation advanced is that the more rapid ions are atomic actinium A and B, and that the slower ion is formed when the more rapid ion attaches itself to a neutral molecule (presumably air). A comparison of the results in the case of these heavy ions with those in the case of the air and C${\mathrm{O}}_2$ ions shows that the mobility of an ion is practically independent of its mass.